1. Field of the Invention
This invention relates to a recording apparatus and, more particularly, to a recording apparatus having a detent mechanism which operates to supply a recording sheet and an ink ribbon and which also serves as a driving power source.
2. Description of the Prior Art
Referring first to FIG. 5, a typewriter which is an example of this type of conventional recording apparatus is provided with a carriage 1 having a printing head and capable of accommodating an ink ribbon, and a printer mechanism 2 which includes a driving power source for feeding a sheet and the ribbon and a transmission mechanism for this operation.
FIG. 6 schematically illustrates details of the printer mechanism 2, including a motor 3, a clutch 4, a platen 5 for supplying a sheet and forming the printing surface, and a torque shaft 6 for transmitting power to feed the ink ribbon provided in the carriage 1. A gear 3A which is attached to a rotary shaft of the motor 3 meshes with a clutch gear 4A which is rotatably supported around a shaft 4C extending from the clutch 4. As the clutch gear 4A is moved in response to the movement of the clutch 4, it meshes with a torque shaft gear 14 or with a platen gear 12 which is connected to a rotary shaft 5B of the platen 5 coaxially therewith. A torque shaft pulley 6A which is connected to the torque shaft gear 14 coaxially therewith is engaged, via a belt 7, with a torque shaft pulley 6B which is connected to the torque shaft 6 coaxially therewith. The torque of the motor 3 is thereby transmitted to the torque shaft 6 or to the platen 5 by suitably changing over the clutch 4.
As the platen 5 rotates, a printing sheet 5A wound around the platen 5 is fed line by line. The ribbon on the carriage 1 is moved by the movement of the torque shaft 6 by any conventially known means. For example, a pair of bevel gears ay be used wherein a first bevel gear is arranged integrally with shaft 6 and a second bevel gear is arranged integrally with the ribbon winding shaft, the second bevel gear engaging the first bevel gear. Shaft 6 would rotate the first bevel gear which action rotates the second bevel gear to move the ribbon.
A solenoid 8 has a shaft 8A which is engaged with one end of a solenoid lever 13. The solenoid lever 13 is swingably supported at this end. The other end of solenoid lever 13 engages recess 4B of clutch 4. Therefore, the solenoid 8 can move the lever 13 and, hence, the clutch 4 by the axial movement of the shaft 8A, thereby selecting the portion to which the torque is transmitted.
FIG. 7 shows in perspective an example of a conventional detent mechanism. This mechanism is disposed at an end of the platen 5 in a position opposite to that of the printer mechanism 2 relative to this platen 5. The detent mechanism is constituted by a detent gear 10 coaxial with the shaft 5C of the platen 5, and a plate spring 9 capable of engaging with the detent gear 10.
The plate spring 9 has a bent end portion which engages with the detent gear 10 by entering one of root portions thereof. The movement of the platen 5 is limited by the urging force of the plate spring 9 so as to set the printing line pitch. As the platen 5 rotates to feed a sheet 5A, the detent gear 10 rotates and the bent end portion of the plate spring 9 climbs over a tooth of the gear 10 and enters in an adjacent root portion.
However, in a conventional arrangement, there is the problem of noise occurring when the plate spring 9 climbs over a tooth of the detent gear 10 at the time of sheet feeding, and a problem of inaccuracy of setting of the sheet feeding pitch due to a low accuracy of engagement between the bent end portion of the plate spring 9 and the detent gear 10.